1. Technical Field
This invention relates generally to an audio volume control process and circuit using a pulse width modulation (PWM) signal that is generated with a variable duty ratio according to the users operation, and regulates the output level of the audio signal.
2. Related Art
Audio output appliances, like television sets and audio systems, usually amplify and output the audio signal with an amplifier. The audio output appliances have built-in volume controllers, and the audio signal level is regulated and put out according to the volume controller operated by the user.
Recently, with the development of computer technology, multi-media technology has employed such a technique so that various audio signals are put out with an audio card in the computer system. An example of this is found in various computer games, wherein audio signals are produced according to the process of the game with audio cards. Exemplars of recent efforts in the art are found among the designs and processes described, for example, in U.S. Pat. No. 5,666,431 to Gillespie et al, entitled volume Control For A Personal Computer Internal Speaker, U.S. Pat. No. 5,150,415 to Jaffee et al, entitled Volume Control Circuit Using Pulse Modulation, U.S. Pat. No. 4,724,396 to Taylor Jr., et al., entitled Digital Audio Amplifier, U.S. Pat. No. 4,433,416 to Kojima, entitled PCM Signal Processor, U.S. Pat. No. 4,390,834 to Ohshima, entitled Digital Volume Control, U.S. Pat. No. 4,371,840 to Yokoyama, entitled Gain Control Circuit For Pulse Width Modulation Amplifier, U.S. Pat. No. Re. 30,482 to Whitlock, entitled Pulse Code Modulated Digital Audio system, entitled Pulse Code Modulated Digital Audio System, and U.S. Pat. No. 4,030,129 to Whitlock, entitled Pulse Code Modulated Digital Audio system.
While playing compact disks (CDS) or audio or video compact disks (VCDs) in the compact disk-read only memory (CD-ROM) drive attached to a computer system, the audio signal from the CDS or VCDs will be put out from the audio card. As the audio cards putting out the audio signal have been attached to the computer system, the monitor, which has been used only as the output screen or display of the computer system, not only expresses a certain image, but also amplifies the audio signal provided by the computer system and puts it out through a speaker. The monitor also has a built-in volume controller regulating the volume output, and the level of the audio signal will be varied and be put out as a user regulates the volume controller. Thus, a variable resistor has conventionally been used as a volume controller in order to control the level of the audio signal put out by the audio output appliances and the computer system.
I have found that such conventional variable resistors having been burdened by disadvantages when used as a volume controller. For example, as explained in more detail below, such variable resistors are such that is difficult to regulate the signal level of audio signals passing through such variable resistors. In addition, due to errors associated with the variable resistors, a uniform signal-to-noise ratio is difficult to obtain. Furthermore, as such variable resistors are used over a period of time, they can become attenuated or can cause noise due to dust or humidity. Finally, in such conventional arrangements, the user can be disturbed due to the occurrence of a popping noise when the speakers are muted.